Tobamovirus

VIRION

Non-enveloped, rigid helical rods with a helical symmetry. Virion is about 18 nm in diameter, and 300-310 nm in length.

GENOME

Monopartite, linear, ssRNA(+) genome of 6.3-6.5 kb. The 3'-terminus has a tRNA-like structure. The 5' terminus has a methylated nucleotide cap (m7G5’pppG).

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and viral messenger RNA. The 5'-proximal ORFs are directly translated to produce the viral constituents of the replicase complex. RdRp is translated through suppression of termination at the end of ORF1. The small replicase is involved in replication and acts as a suppressor of RNA silencing. The movement proteins and the capsid protein are expressed from separate subgenomic mRNAs.

REPLICATION

CYTOPLASMIC

Virus penetrates into the host cell.

Uncoating, and release of the viral genomic RNA into the cytoplasm.

The viral RNA is translated to produce the two proteins necessary for RNA synthesis (replication and transcription).